Approximately 12,000 kidney transplants are performed annually in the United States. Despite the availability of potent immunosuppressive agents, graft rejection remains the main complication of renal transplantation. For example, approximately 50% of all renal allograft recipients are thought to suffer at least one episode of graft rejection. The likelihood of kidney loss due to rejection is highest during the first year post transplant (10–20%), but a small proportion (3–5%) of kidneys are rejected each year even after the first year.
Statistics indicate that graft rejection is often not detected early enough in the rejection episode to allow initiation of countervailing treatment in time to prevent the organ rejection with immunosuppressive agents at a time when the rejection process could be effectively halted and/or prevented altogether.
The diagnosis of acute allograft rejection is classically based on the presence of one or more symptoms. For example, symptoms of acute allograft rejection include weight gain, reduced urine output, increased serum creatine concentrations, hypertension, fever, and graft enlargement and tenderness. However, the use of these symptoms alone to detect rejection is not adequate. Currently, most transplant rejection episodes are detected by periodically measuring the function of the transplanted kidney, for example by using biochemical tests such as assays that measure serum creatine concentrations.
Presently, renal biopsy remains the most definitive test to specifically diagnose renal allograft rejection. However, this method has major limitations. For example, since the biopsy procedure itself has complications, and since a portion of the renal transplant is removed during each biopsy, transplant biopsy cannot be performed on a routine or even frequent basis to monitor renal allograft rejection. In addition, the invasive nature of a renal biopsy is both uncomfortable and inconvenient for patient subjects. Accurate interpretation of the renal transplant biopsy also demands the expertise of a pathologist with extensive experience in analyzing a biopsy sample for evidence of renal transplant rejection. Hence, renal biopsies are reserved for those patients that demonstrate other clinical and/or laboratory evidence of renal allograft rejection, thus limiting its use or potential use in detecting early graft rejection.
A method for the early detection and/or prediction of graft rejection would thus be an important clinical tool for maintaining the viability of a transplanted organ.